b 1. Field of the Invention
This invention pertains to systems for ejecting small quantities of liquid upon command, for use in apparatus such as ink jet printers and recorders. It relates particularly to systems in which the energy required to eject a droplet is obtained from an electric pulse acting through an electroacoustic transducer, no pump or equivalent source of pressure being employed during operation. Such systems may be described as passive systems.
2. Description of the Prior Art
Passive droplet ejecting systems are described in U.S. Pat. Nos. 3,452,360 to Williamson, 3,683,212 to Zoltan; 3,708,798 to Hildenbrand et al.; 3,747,126 to Stemme; 3,787,884 to Demer and 3,832,579 to Arndt. Very small quantities of air entrapped in these systems cause erratic and unreliable operation. Clearing such systems of air is difficult because generally the orifice size is so small that even relatively large priming pressures cannot produce sufficient flow to dislodge small air pockets that adhere in small crevasses or even to relatively smooth surfaces.